1. Field of the Invention
The present invention relates to an apparatus for the retrieval of particulate matter from a fixed bed reactor. More particularly, the invention relates to a device for safely withdrawing samples of particulate material such as catalyst from a reaction vessel while it is operating at sub or super atmoshperic conditions without altering such conditions.
2. Description of the Prior Art
A number of prior art apparatuses have been devised for the retrieval of samples of particulate matter from fixed bed reactors. U.S. Pat. No. 2,973,645, to W. W. Grimes et al discloses a device which functions by rotation of an inner catalyst sample enclosure within an external guide tube. The device shown appears to be designed for sampling of catalyst near the bottom of the reactor. A tubular screen is extended upward into the catalyst bed from the top of the sample device. Since the cylindrical screen will be filled with catalyst when the vessel is filled, samples taken of catalyst will be from the level at the entrance to the sample closure. If the volume of the sample is small compared to the volume within the cylindrical screen, a representative sample from the level where the cylindrical screen ends could not be possible.
This type screen construction most likely would suffer severe distortion since the rather flexible screen would tend to thermally expand upward but be restrained by the catalyst, and accordingly, would be deformed and possibly rendered inoperative. Rotating the inner component of the sampler also requires that the shaft be sized for torsion. If high friction forces are involved torsional distortion is likely due to the shaft being weakened by the catalyst ports provided.
U.S. Pat. No. 3,129,590 to J. R. B. Ellis also discloses a device which terminates within the cayalyst bed with the catalyst sample being retrieved by rotation of an inner member. The device would be susceptible to deformation and/or malfunction since the sampler is terminated in the bed which will restrain the device from thermal movement when it expands. The probe is also angled inward which tends to further increase deformation due to a horizontal component of thermal expansion. Any deformation would lead to increased torsional friction due to interaction between the outer tube and inner member.
U.S. Pat. No. 3,348,419 to G. E. Addison also uses rotation between an inner and outer tube for retrieving of a catalyst sample through an elongated slot (port). The device terminates in the bed which makes the probe susceptible to deformation from restraint of the bed similar to that of J. R. B. Ellis.
U.S. Pat. No. 3,561,274 to W. M. Haunschild discloses a device which operates by using a rotating disc on top where a hole in the disc permits catalyst to flow into the probe when its port is in alignment with the hole in the top disc. This device must terminate in the catalyst bed and for this reason it is susceptible to deformation and malfunction similar to the patents by Addison, Ellis, and Hensel. Furthermore, the disc must be turned while it is buried in catalyst. This increases the friction considerably and makes the mechanism vulnerable to torsional shaft failure.
U.S. Pat. No. 3,442,138 to W. C. Hensel discloses a device which utilizes a catalyst sample capsule to limit the amount of sample to be taken. It operates by axial displacement and two versions of internal sample capsule are shown. The device terminates in the bed which makes it susceptible to deformation and malfunction similar to the devices by G. E. Addison and J. R. B. Ellis.
U.S. Pat. No. 3,319,469 to R. L. Hartung discloses a device which samples catalyst from a number of catalyst beds in one vessel. This is achieved by axial movement of an inner tube within an outer tube, each provided with coinciding port openings. Because of the extension traverse that the device must handle, it is possible that the vessel would have to be elevated above that normally used to make room for the sampling device retrieving section. The positioning of the inner probe also requires that the inlet port for sample taking and outlet port for retrieving the sample at each bed level must be accurately aligned since nonalignment of the ports, e.g. 3/8" diameter holes will cause malfunction of the probe. All of this must be done from an external position below the vessel. When taking into consideration thermal expansion, i.e. the upward movement of the probe assembly the uppermost point would expand approximately 4 inches upward. If the inner tube did not move this amount, it would be impossible to insure from an external position that the port in the inner tube was in alignment with the port in the external tube of the probe. The device, therefore, would be extremely complex and impractical or difficult to use with assurance of satisfactory function. The device extends past the upper level of the bed and this will reduce the tendency for buckling since the catalyst bed only restrains thermal movement of the probe by axial friction of catalyst against the outer surface of the probe.
All of the devices described in prior art patents exhibit undesirable characteristics which limit their effective utilization for the retrieval of particulate samples from fixed bed reactors without interrupting the reaction process. Now, in accordance with the present invention, an apparatus has been devised where consideration has been given to avoiding thermal and bed weight distortion by limiting sampling to one bed level, thereby limiting overall length, and by letting the probe extend vertically through the bed, terminating in an empty space above the bed, even though the inlet port, i.e. sampling location may be located at any point in the bed. The device functions by axial displacement of an inner tube with respect to an outer tube. Since only one sample location is considered, the device is less likely to malfunction. The extension above the bed level permits venting of the probe and avoids the deformation associated with the restraint of the bed weight of prior art devices. The device is adaptable for installation in existing units without requiring special vessel shell nozzles and can be assembled in prefabricated sections. Thus, the device exhibits the beneficial characteristics of avoiding thermal distortion, bed weight distortion, simplicity, and ease of installation in existing units.